Thouless pumping in disordered photonic systems

Integrated optics: combating disorder Research into the effect of temporally-modulated pumping in coupled optical waveguides may aid the design of future on-chip slow light devices. The result could be designs which are more robust against disorder and fabrication imperfections. Alexander Cerjan and coworkers from Pennsylvania State University and the University of Pittsburgh in the USA studied adiabatic pumping, also known as Thouless pumping, in a one-dimensional array of laser-written evanescently-coupled waveguides in borosilicate glass. Nearly quantized topological transport of light was observed, even in the presence of disorder which was introduced by a variation in the spacing between neighboring waveguides. The adiabatic pumping was achieved by dynamically modulating the refractive index of the waveguide array (where temporal modulation was mapped to spatial variations). Future research will explore the connection between Thouless pumping and dynamical quantum ratchets. Thouless charge pumping protocols provide a route for one-dimensional systems to realize topological transport. Here, using arrays of evanescently coupled optical waveguides, we experimentally demonstrate bulk Thouless pumping in the presence of disorder. The degree of pumping is quite tolerant to significant deviations from adiabaticity as well as the addition of system disorder until the disorder is sufficiently strong to reduce the bulk mobility gap of the system to be on the scale of the modulation frequency of the system. Moreover, we show that this approach realizes near-full-unit-cell transport per pump cycle for a physically relevant class of localized initial system excitations. Thus, temporally pumped systems can potentially be used as a design principle for a new class of modulated slow-light devices that are resistant to system disorder.